Absorbent core with elongate liquid holding formation

ABSTRACT

An absorbent core comprises an elongate liquid holding formation with a peripheral edge. The liquid holding formation has a surface formed with at least one channel extending longitudinally in the core for distributing liquid lengthwise along the core. The channel has longitudinally opposite ends spaced longitudinally inward from the peripheral edge of the liquid holding formation to inhibit the flow of liquid in the channels past the peripheral edge of the liquid holding formation.

REFERENCE TO RELATED APPLICATIONS

This divisional patent application claims priority from U.S. patentapplication Ser. No. 10/207,929 filed on Jul. 30, 2002, the entirety ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to an absorbent core of air formedfibrous material that can be used for applications such as disposablediapers, child's training pants, feminine care articles, incontinencearticles, and the like.

In the general practice of forming fibrous web materials, such as airformed fibrous webs, it has been common to use a fibrous sheet ofcellulosic or other suitable absorbent material which has been fiberizedin a conventional fiberizer, or other shredding or comminuting device,to form discrete fibers. In addition, particles of superabsorbentmaterial have been mixed with the fibers. The fibers and superabsorbentparticles have then been entrained in an air stream and directed to aforaminous forming surface upon which the fibers and superabsorbentparticles have been deposited to form an absorbent fibrous web. Anabsorbent core formed in this fashion has a liquid holding formationwhich is intended to be the primary repository for liquid to be held bythe absorbent core. Thus, the liquid holding formation hasconventionally been formed to have a greater amount of fibrous andsuperabsorbent material (SAM) than surrounding regions and is generallythicker than the surrounding regions of fibrous material.

The forming surfaces used in such systems have been constructed with aperforated plate or wire screen grid and can typically employ apneumatic flow mechanism, such as vacuum suction apparatus, to produce apressure differential across the forming surface. The pressuredifference causes an airflow through the openings or perforations in theplate or screen of the forming surface. The use of vacuum suction todraw the air-entrained fiber stream onto the forming surface, and passthe airflow through the forming surface is presently employed inhigh-speed commercial operations. In operation, fibrous material isdeposited on the forming surface as it passes through a chamber of thefluent fibers, forming a layer of fibrous material on the formingsurface. As the forming layer increases in basis weight (i.e., weight ofdeposited fiber and SAM per unit area) resistance to air flow throughthe layer increases. One problem which arises as a result of increasedresistance is inadequate deposition of fiber in the area which forms theliquid holding formation. Stated another way, the liquid holdingformation may not have a sufficiently higher basis weight than thesurrounding regions. The problem can be particularly acute when the areain which material is to be deposited is narrow. There are also problemsassociated with increased flow resistance such as high weightvariability in the absorbent core, fiber damaged caused by excessiveretention in the fiberizer, and poor strength caused by insufficiententanglement of fibers in the absorbent core.

The liquid holding formation is typically formed through the provisionof a pocket in the forming surface. It has been found that instead ofdepositing fibrous material to a greater depth in the pocket the depthof material often is nearly the same as in the shallower surroundingregions. Typically, the absorbent core is cut or scarfed after formingon the forming surface so that the surrounding areas end up with alesser thickness than the region of the liquid holding formation.However, there is often a marked dip in the scarfed surface of thefinished absorbent core in the liquid holding formation area indicatingthat less than a full desired thickness of fibrous material has beendeposited. The reduction in the amount of fibrous material (andsuperabsorbent material) corresponds to a reduction in the quantity ofliquid which can be held by the liquid holding formation and theabsorbent core. Attempts to remedy this and other problems associatedwith air flow by control of the vacuum pressure on the forming surfacehave been complicated and difficult to control.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an absorbent core comprises anelongate liquid holding formation with a peripheral edge. The liquidholding formation has a surface formed with at least one longitudinallyextending channel in the core for distributing liquid lengthwise alongthe core. The channel has longitudinally opposite ends spacedlongitudinally inward from the peripheral edge of the liquid holdingformation to inhibit the flow of liquid in the channels past theperipheral edge of the liquid holding formation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, side elevation of apparatus for forming an airformed fibrous web;

FIG. 1A is a schematic perspective of a drum of the apparatus;

FIG. 2 is a fragmentary cross-section the apparatus of FIG. 1;

FIG. 3 is a bottom perspective of a form member of the apparatus;

FIG. 4 is a top plan view of the form member;

FIG. 5 is a fragmentary section taken in the plane including line 5-5 ofFIG. 1A;

FIG. 6 is a cross section of a scarfed absorbent core formed byapparatus of the present invention;

FIG. 7 is a top plan view of a second, modified form member;

FIG. 8 is a fragmentary section similar to FIG. 5, but showing thesecond, modified form member of FIG. 7;

FIG. 9 is a fragmentary section similar to FIG. 5, but showing a third,modified form member;

FIG. 10 is another absorbent core.

Corresponding reference characters indicated corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1, 1A and 2, for purposes of the present descriptionthe apparatus has a machine-direction MD which extends generally in thedirection of motion of the machine, a lateral cross-direction CD whichextends transversely to the machine direction, and a z-direction Z. Forthe purposes of the present disclosure, the machine-direction MD is thedirection along which a particular component or material is transportedlengthwise along and through a particular, local position of theapparatus. The cross-direction CD lies generally within the plane of thematerial being transported through the process, and is transverse to thelocal machine-direction MD. The z-direction Z is aligned substantiallyperpendicular to both the machine-direction MD and the cross-directionCD, and extends generally along a depth-wise, thickness dimension of thematerial.

Apparatus 1 constructed according to the principles of the presentinvention for forming a fibrous web 3 can include a movable, foraminousforming surface 5 extending around the circumference of a drum 7 (thereference numerals designating their subjects generally). The drum 7 ismounted on a shaft 9 connected by bearings 11 to a support 13. As shownin FIG. 2, the drum includes a circular wall 15 connected to the shaft 9for conjoint rotation therewith. The shaft 9 is driven in rotation by asuitable motor or line shaft (not shown) in a counterclockwise directionas seen in FIG. 1. The wall 15 cantilevers the forming surface 5 and theopposite side of the drum 7 is open. A vacuum duct 17 located radiallyinwardly of the forming surface extends over an arc of the druminterior. The vacuum duct 17 has an arcuate, elongate entrance opening19 under the foraminous forming surface 5, as will be described in moredetail hereinafter, for fluid communication between the vacuum duct andthe forming surface. The vacuum duct 17 is mounted on and in fluidcommunication with a vacuum conduit 21 connected to a vacuum source 23(represented diagrammatically in FIG. 2). The vacuum source 23 may be,for example, an exhaust fan. The vacuum duct 17 is connected to thevacuum supply conduit 21 along an outer peripheral surface of theconduit, and extends circumferentially of the conduit. The vacuum duct17 projects radially outwardly from the vacuum conduit 21 toward theforming surface 5 and includes axially spaced side walls 17A andangularly spaced end walls 17B. The shaft 9 extends through the wall 15and into the vacuum supply conduit 21 where it is received in a bearing10 connected to a brace 12 within the conduit. The bearing 10 is sealedwith the vacuum supply conduit 21 so that air is not drawn in around theshaft 9 where it enters the conduit. The brace 12 and entire conduit 21are supported by an overhead mount 14.

A drum rim 18 is mounted on the wall 15 of the drum 7 and has amultiplicity of holes over its surface area to provide a substantiallyfree movement of air through the thickness of the rim. The rim 18 isgenerally tubular in shape and extends around the axis of rotation ofthe shaft 9 near the periphery of the wall 15. The rim 18 iscantilevered away from the drum wall 15, and has a radiallyinward-facing surface positioned closely adjacent to the entranceopening 19 of the vacuum duct 17. To provide an air resistant sealbetween the rim 18 and the entrance opening 19 of the vacuum duct 17,rim seals 20 are mounted on the inward-facing surface of the rim 18 forsliding sealing engagement with the walls 17A of the vacuum duct. Seals(not shown) are also mounted on the end walls 17B of the vacuum duct 17for sliding sealing engagement with the inward-facing surface of the rim18. The seals may be formed of a suitable material such as felt topermit the sliding sealing engagements.

The apparatus 1 further includes a forming chamber 25 through which theforming surface 5 is movable. The forming chamber 25 has an entrance 27where the forming surface 5 enters the chamber substantially free offibrous material, and an exit 29 where the forming surface leaves thechamber substantially filled with fibrous material. A fiberizer 31provides fibrous material into the forming chamber 25, and the vacuumsource 23 (FIG. 2) creates a vacuum pressure in the vacuum duct 17relative to the interior of the chamber 25. As the forming surface 5enters and then traverses through the forming chamber 25, the componentmaterials of the fibrous web 3 are operatively carried or transported byan entraining air stream that is drawn through the forming surface 5.The pressure differential across the forming surface 5 causes the fluentfibers in the chamber 25 to be drawn to the forming surface.

The selected fibrous material may be suitably derived from a batt B ofcellulosic fibers (e.g., wood pulp fibers) or other source of naturaland/or synthetic fibers, which has been disintegrated, in a manner wellknown in the art, to provide an operative quantity of individual, loosefibers. The fiberizer 31 receives a selected web-forming material,converts the web-forming material into individual fibers, and deliversthe fibers into the forming chamber 25. In the illustratedconfiguration, the fiberizer 31 can be a rotary hammer mill or arotatable picker roll. However, it is to be understood that fibers maybe provided in other ways by other devices within the scope of thepresent invention. Suitable fiberizers are available from PaperConverting Machine Company, a business having offices located in GreenBay, Wis., U.S.A.

Other component materials for producing the fibrous web 3 may also bedelivered into the forming chamber 25. For example, particles or fibersof superabsorbent material may be introduced into the forming chamber 25by employing conventional mechanisms, such as pipes, channels,spreaders, nozzles and the like, as well as combinations thereof. In theillustrated embodiment, the superabsorbent material is delivered intothe forming chamber 25 by employing a schematically represented deliveryconduit and nozzle system 33. The fibers, particles and other desiredweb material may be entrained in any suitable gaseous medium.Accordingly, any references herein to air as being the entraining mediumshould be understood to be a general reference which encompasses anyother operative entraining gas. Superabsorbent materials are well knownin the art, and are readily available from various suppliers. Forexample, FAVOR SMX 880 superabsorbent is available from Stockhausen,Inc., a business having offices located in Greensboro, N.C., U.S.A.; andDrytech 2035 is available from Dow Chemical Company, a business havingoffices located in Midland, Mich., U.S.A.

The stream of fluent fibers and particles pass through the formingchamber 25 for deposition onto the forming surface 5. The formingchamber 25 can serve to direct and concentrate the air-entrained fibersand particles, and to provide a desired velocity profile in theair-entrained stream of fibers and particles. Typically, the formingchamber 25 is supported by suitable structural members, which togetherform a support frame for the forming chamber. The frame may be anchoredand/or joined to other suitable structural components, as necessary ordesirable. The construction and operation of such forming chambers 25 iswell known and will not be described in further detail herein. Insteadof applying the fibers (and SAM) directly to the forming surface, it isknown to place a porous substrate over the forming surface on which thefibers are deposited. Suitable substrates may, for example, be formedfrom tissue, spunbond, nonwoven or woven materials. A web 26 ofsubstrate is shown in phantom in FIG. 1 to extend from a roll 28 intothe entrance 27 of the forming chamber 25. The roll 28 can be held andthe web 26 fed out by suitable delivery device (not shown in itsentirety) as is known in the art. A roller 30 of the delivery device isshown for guiding the web 26 into the entrance 27. The web 26, whenused, overlies the forming surface 5 so that fibers and superabsorbentmaterial are deposited on the web rather than directly on the formingsurface 5. The vacuum causes the web 26 to conform to the shape of theforming surface 5. The use of such substrates desirably reduces theamount of fiber which passes completely through the forming surface 5because individual pores of the substrate are smaller than the openingsin the forming surface. However for simplicity, the illustratedembodiment will be described hereinafter without reference to thesubstrate web 26.

The forming surface 5 is illustrated as being part of the forming drum7, but it is to be understood that other techniques for providing theforming surface 5 may also be employed without departing from the scopeof the present invention. For example, the forming surface 5 may beprovided by an endless forming belt (not shown). A forming belt of thistype is shown in U.S. Pat. No. 5,466,409, entitled FORMING BELT FORTHREE-DIMENSIONAL FORMING APPLICATIONS by M. Partridge et al. whichissued on Nov. 14, 1995.

The foraminous forming surface 5 is defined in the illustratedembodiment by a series of form members 34 which are arranged end-to-endaround the periphery of the forming drum 7 and independently attached tothe drum. As may be seen in FIG. 1A, the form members 34 each define asubstantially identical pattern 36 in which fibrous material isdeposited. The patterns 36 correspond to a desired shape of individualabsorbent cores 38 (one of which is shown in FIG. 6) which repeats overthe circumference of the drum. However, partially repeating ornon-repeating pattern shapes may be used with the present invention.Under the influence of the vacuum source 23, a conveying air stream isdrawn through the foraminous forming surface 5 into the vacuum duct 17on the interior of the forming drum 7, and is subsequently passed out ofthe drum through the vacuum supply conduit 21. As the fluent fibers andparticles impinge the foraminous forming surface 5, the air component ispassed through the forming surface and the fibers-particles component isretained by the forming surface to form a nonwoven fibrous web 3thereon. Subsequently, with the rotation of the drum 7, the formed web 3is removed from the forming surface 5.

The drum 7 carrying the air formed fibrous web 3 deposited on theforming surface 5 in the forming chamber 25 passes out of the chamberthrough the exit 29 to a scarfing system, generally indicated at 35 inFIG. 1, where excess thickness of the fibrous web can be trimmed andremoved to a predetermined extent. The scarfing system includes ascarfing chamber 37 and a scarfing roll 39 which is positioned withinthe scarfing chamber. The scarfing roll 39 abrades excess fibrousmaterial from the fibrous web 3, and the removed fibers are transportedaway from the scarfing chamber 37 with a suitable discharge conduit (notshown), as well known in the art. The removed fibrous material may, forexample, be recycled back into the forming chamber 25 or the fiberizer31, as desired. Additionally, the scarfing roll 39 can rearrange andredistribute the web material along the longitudinal machine-directionMD of the web 3 and/or along the lateral cross-direction CD of the web.The profile of the web made by a scarfing roll may be flat (as withscarfing roll 39), but also may be shaped or irregular as desired byselection and arrangement of teeth (not shown) on the scarfing roll.

The rotatable scarfing roll 39 is operatively connected and joined to asuitable shaft member, and is driven by a suitable drive system (notshown). The drive system may include any conventional apparatus, such asprovided by a dedicated motor, or a coupling, gear or other transmissionmechanism operatively connected to the motor or other drive mechanismemployed to rotate the forming drum 7. The scarfing roll system 35 canprovide a conventional trimming mechanism for removing or redistributingany excess, z-directional thickness of the air formed fibrous web thathas been deposited on the forming surface 5. The scarfing operation canyield a fibrous web having a selected contour on a major face-surface ofthe fibrous web that has been contacted by the scarfing roll 39. Thesurface of the scarfing roll can be adjusted to provide a desiredcontour along the scarfed surface of the fibrous web 3. In theillustrated embodiment, the scarfing roll 39 can, for example, beconfigured to provide a substantially flat surface along the scarfedsurface of the fibrous web 3. The scarfing roll 39 can optionally beconfigured to provide a non-flat surface. The scarfing roll 39 isdisposed in spaced adjacent relationship to the forming surface 5, andthe forming surface is translated past the scarfing roll by rotation ofthe drum 7.

In the illustrated embodiment, the scarfing roll 39 rotates in adirection which moves a contacting surface of the scarfing roll in acounter-direction that is opposite the rotation of the drum 7 and themovement direction of the air formed fibrous web 3. Alternatively, thescarfing roll 39 may be rotated so that the roll surface moves in thesame direction as the forming surface 5 on the forming drum 7. In eithersituation, the rotational speed of the scarfing roll 39 should besuitably selected to provide an effective scarfing action against thecontacted surface of the formed fibrous web 3. In like manner, any othersuitable trimming mechanism may be employed in place of the scarfingroll 39 assembly to provide a cutting or abrading action to the airformed fibrous web by a relative movement between the fibrous web 3 andthe selected trimming mechanism.

After the scarfing operation, the portion of the forming surface 5 thatis carrying the air formed fibrous web 3 can be moved to a release zoneof the apparatus 1. In the release zone vacuum causes the web 3 totransfer from the forming surface 5 onto a conveyor indicated generallyat 41. The release can be assisted by the application of air pressurefrom the interior of the drum 7. The conveyor 41 receives the formedfibrous web 3 from the forming drum 7, and conveys the web to acollection area or to a location for further processing (not shown).Suitable conveyors can, for example, include conveyer belts, vacuumdrums, transport rollers, electromagnetic suspension conveyors, fluidsuspension conveyors or the like, as well as combinations thereof. Inthe illustrated embodiment, the conveyor 41 includes an endless conveyorbelt 43 disposed about rollers 45. A vacuum suction box 47 is locatedbelow the conveyor belt 43 to remove the web 3 from the forming surface5. The belt 43 is perforate and the vacuum box 47 defines a plenumbeneath the portion of the belt in close proximity to the formingsurface so that a vacuum is communicated to the fibrous web 3 on thedrum 7. Removal of the web 3 can alternatively be accomplished by theweight of the web, by centrifugal force, by mechanical ejection, bypositive air pressure or by some combination or by another suitablemethod. The positive air pressure can be produced, for example, by asource of compressed air (not shown) such as a fan which generates apressurized air flow that exerts a force directed outwardly through theforming surface 5. The removed fibrous web includes an interconnectedseries of absorbent cores, and each body has a selected surface contourwhich substantially matches the contour provided by the correspondingportions of the forming surface 5 upon which each individual pad wasformed. It is also possible to contour the scarfed side of the web 3.

Suitable forming drum systems for producing air formed fibrous webs arewell known in the art. For example, see U.S. Pat. No. 4,666,647 entitledAPPARATUS AND METHOD FOR FORMING A LAID FIBROUS WEB by K. Enloe et al.which issued May 19, 1987; and U.S. Pat. No. 4,761,258 entitledCONTROLLED FORMATION OF LIGHT AND HEAVY FLUFF ZONES by K. Enloe whichissued Aug. 2, 1988; the entire disclosures of which are incorporatedherein by reference in a manner that is consistent herewith. Otherforming drum systems are described in U.S. Pat. No. 6,330,735, entitledAPPARATUS AND PROCESS FOR FORMING A LAID FIBROUS WEB WITH ENHANCED BASISWEIGHT CAPABILITY by J. T. Hahn et al. which issued Dec. 18, 2001, andU.S. patent application Ser. No. 09/947,128, entitled MULTI-STAGEFORMING DRUM COMMUTATOR by D. P. Murphy et al., filed Sep. 4, 2001(attorney docket No. 16,632), the entire disclosures of which isincorporated herein by reference in a manner that is consistentherewith. Examples of techniques which can introduce a selected quantityof superabsorbent particles into a forming chamber are described in U.S.Pat. No. 4,927,582 entitled METHOD AND APPARATUS FOR CREATING AGRADUATED DISTRIBUTION OF GRANULE MATERIALS IN A FIBER MAT by R. E.Bryson which issued May 22, 1990; the entire disclosure of which isincorporated herein by reference in a manner that is consistentherewith. It will be appreciated that the description of the drum 7shown in the drawings is exemplary, as other configurations (includingthose not having a drum for carrying the foraminous forming surface 5)may be employed to produce the fibrous web 3.

Referring now to FIG. 3, a single form member 34 is shown as removedfrom the drum 7. As used herein, the term “form” can refer to a singleform member 34 or to a collection of form members, such as the formmembers which extend around the complete circumference of the drum 7.Moreover, it is envisioned that a single form member (not shown)extending around the entire circumference of the drum 7 could beemployed. The illustrated form member 34 comprises outer side walls 51connected to end walls 53 to form a rectangular frame. The side walls 51are curved along their length to match the arc of the drum 7 over whichthe individual form members 34 will extend. Transverse walls 55 extendbetween the side walls 51 and longitudinal walls 57 extend between theend walls 53 inside the frame. The frame supports the forming surface 5which in the illustrated embodiment comprises a honeycombed support 59and a thin, perforated plate 61 (see FIG. 5). The support 59 andperforated plate 61 have the same upper surface shape. The support 59underlies and provides strength for the perforated plate 61 to hold itin a fixed configuration under the load applied by the vacuum. Thesupport 59 permits air to pass freely through it by virtue of therelative larger openings of its honeycomb structure. The openings canhave any desired cross-sectional shape, such as circular, oval,hexagonal, pentagonal, other polygonal shape or the like, as well ascombinations thereof, and need not be in a honeycomb arrangement. Suchsupport structures are well known in the art, and can be composed ofvarious materials, such as plastic, metal, ceramics and the like, aswell as combinations thereof. The smaller holes in the perforated plate61 also allow passage of air, but are sized to capture the fibrousmaterial and prevent its passage through the forming surface 5. Theperforate plate 61 may be replaced by a screen, a wire mesh, a hard-wirecloth or the like, as well as combinations thereof. It is envisionedthat if a sufficiently rigid, self-supporting material could be foundfor the perforate plate 61, the support 59 could be omitted.

Masking plates 63 are attached to the radially outwardly facing surfaceof the form member 34 to mask portions of the perforated plate 61 andsupport 59 to prevent air from passing through the masked portions andhence prevent deposition of fibrous material. The patterns 36 aredefined by the shape of the masking plates 63. The form member 34 ismounted on the drum 7 by a pair of wings 65 attached to and extendinglaterally outwardly from respective side walls 51. When applied to thedrum 7 as shown in FIG. 2, the wings 65 of the form member 34 overlierespective, axially spaced mounting rings 67 mounted on the rim 18 atits opposite lateral edges. The form member 34 is releasably secured tothe mounting rings 67 by bolts 69 passing through elongate openings 71in the wings and threadably received in holes (not shown) formed in therings. The elongation of the openings 71 allows some variation in thecircumferential position of the form member 34, facilitating placementof the forming members on the drum 7.

Referring now to FIGS. 4 and 5 a single form member 34 from the drum 7is shown. The forming surface 5 has a length in the machine direction MDand a width in the cross direction CD and is shaped to include a firstsection 75 at a first depth below the top surface of the masking plate63. The first section 75 is relatively shallow and planar inconfiguration for forming a thinner layer of fibrous material. The firstsection 75 is curved between the ends of the form member 34 incorrespondence with the curvature of the drum 7. Thus rather than beingtruly planar, the first section 75 lies in a smooth surface and issubstantially linear in cross section, as may be seen in FIG. 5. It willbe noted that the cross section is transverse to the extent of the formmember 34 in the machine direction MD. However, the first section 75 maybe irregular or have different depths over its area without departingfrom the scope of the present invention. In that event the “first depth”would be an average depth of the first section 75.

A pocket, indicated generally at 77, includes a bottom surface 79(“second section”) and a transition surface 81 (“third section”)connecting the first section 75 with the bottom surface. The terms “top”and “bottom” are used as convenient descriptors given the orientationsillustrated in the drawings. However, these terms do not require anyabsolute orientation of the subject described. The first section 75 caninclude portions lying on both sides of the bottom surface 79, and inthe illustrated embodiment the first section substantially surrounds thepocket 77. The bottom surface 79 (as shown in FIGS. 4 and 5) has agenerally undulating configuration which is everywhere below the surfacecontaining the first section 75, and is non-linear in cross section.More particularly, the bottom surface 79 has multiple ridges 83extending in the machine direction MD the length of the pocket 77. As aresult of the ridges 83, the (second) depth of the bottom surface 79below the first section 75 varies over the area of the bottom surface.

The ridges 83 located within the pocket 77 greatly increase the surfacearea within the pocket, reducing resistance to air flow (as compared tothe first section 75) and thereby promoting the deposit of more fibrousmaterial. Stated another way with reference being made to FIG. 5, theactual surface area of the bottom surface (or “second section”) 79 isgreater than an area P2 of the bottom surface (or second section) 79projected onto a generally planar surface S lying directly above theforming surface 5. Although the surface S is generally planar, in factit has a curvature corresponding to the curvature of the forming surface5 along its length. The surface area of the bottom surface 79 is measurealong its undulating extent over the ridges 83 and so is clearly largerthan the projected area P2. FIG. 5 also illustrates the projected areaP1 of the first section 75 and the projected area P3 of the transitionsurface (third section) 81 onto the surface S. The projected areas P1and P3 are shown to more particularly delineate the projected area P2.In one embodiment, the actual surface area of the bottom surface 79 isat least about 10% larger than the projected surface area P2.

As a result of the surface area of the bottom surface 79, the depth offibrous material deposited in the pocket 77 is significantly greaterthan in the first section 75. When the fibrous web 3 is scarfed and cutto define absorbent cores like the absorbent core 38 illustrated in FIG.6, a liquid holding formation 38A of the absorbent core has its fullspecified thickness and an upper surface 84 which is substantially flat.In other words, there is no dip in the upper surface 84 of the scarfedabsorbent core 38 in the area of the liquid holding formation 38A causedby inadequate deposition of fibrous material in the pocket 77 of theforming surface 5. The liquid holding formation 38A has a sufficientlyhigh basis weight and entanglement of the fibers in the formation isenhanced. Thus, the strength of the holding formation is enhancedwithout sacrificing the structural integrity of the shallowersurrounding regions. The screen side of the liquid holding formation 38A(i.e., the side which engages the forming surface 5 when formed) isformed by the ridges 83 to have two channels 40 extending the length ofthe pocket 77.

Referring to FIGS. 5 and 6, the surface area of the liquid holdingformation 38A on the screen side of the absorbent core 38 is augmentedby the shape given to it by the ridges 83 of the forming surface 5. FIG.6 illustrates the projection of various surfaces of the absorbent core38 onto a planar surface S′. The projected area of the absorbent core 38which was formed by the bottom surface 79 of the forming surface 5 isindicated at PC2, the projected area of the core which was formed by thefirst section 75 is indicated at PC1, and the projected area of the corewhich was formed by the transition surface 81 is indicated at PC3. Theprojected area PC1 would be about the same as the surface area of thepart of the absorbent core 38 which was formed by the first section 75(in the illustrated embodiment). The projected area PC3 would be lessthan the surface area of the part of the absorbent core 38 formed by thetransitional surface 81. It will be understood that the actual surfacearea of that part of the absorbent core formed by the bottom surface 79will be larger than the projected area PC2 because of the additionalsurface area provided by the channels 40. For example, the surface areaof the part of the absorbent core formed by the bottom surface 79 mightbe 10% larger than the projected area PC2.

A second, modified version of the forming surface 5′ is shown in FIGS. 7and 8. Corresponding parts of the second, modified version of theforming surface 5′ will be indicated by the same reference numerals asfor the first version of the forming surface 5, followed by a prime. Theforming surface 5′ includes a first section 75′ substantially the sameas the first section 75 of the forming surface 5 of FIGS. 4 and 5. Atransition surface 81′ connects the first section 75′ to the bottomsurface 79′. However instead of ridges 83, the bottom surface 79′includes two steps 85 extending in the machine-direction MD of thepocket 77′. The provision of the stepped bottom surface 79′ within thepocket 77′ increases the surface area of the pocket so that more fibrousmaterial will be deposited in the pocket before the region of theperforated plate 61 within the pocket becomes clogged with fibrousmaterial.

A third, modified version of the forming surface 5″ is shown in FIG. 9.Corresponding parts of the third, modified version of the formingsurface 5″ will be indicated by the same reference numerals as for thefirst version of the forming surface 5, followed by a double prime. Theforming surface 5″ includes a first section 75″ substantially the sameas the first section of the forming surface 5 of FIGS. 4 and 5. Howeverinstead of ridges 83 or steps 85, the bottom surface 79″ is domed inshape and is a smooth curve in transverse cross section. The provisionof the dome shape within the pocket 77″ increases the surface area ofthe pocket. In the third, modified version of the forming surface 5″,the transition surface 81″ is located at the boundary between the firstsection 75″ and the bottom surface 79″, but lies in the same smoothsurface as the bottom surface.

It will be readily apparent that various conventional devices andtechniques can be employed to further process the web 3. For example,the web can be debulked at a debulking station. In addition, variousconventional devices and techniques can be employed to sever fibrous web3 into predetermined lengths to provide selected air formed fibrousarticles. The severing system may, for example, include a die cutter, awater cutter, rotary knives, reciprocating knives, energy beam cutters,particle beam cutters or the like, as well as combinations thereof.After severing, the discrete fibrous pads can be transported anddelivered for further processing operations, as desired.

Referring now to FIG. 10, an absorbent core 87 manufactured using a formhaving a forming surface (not shown) of the same general type as theforming surface 5 is shown with its screen side facing up so that itsliquid holding formation 89 projects out of the page. The absorbent core87 is shown in the orientation it would occupy leaving the forming drum(e.g., drum 7), which is inverted from the position in which the core isformed at the top of the drum. The forming surface used to make theabsorbent core 87 has shapes in its pocket so that the screen side ofliquid holding formation 89 of the absorbent core 87 is formed withplural channels 91 extending generally longitudinally of the liquidholding formation. As used herein “generally longitudinally” does notexclude some lateral extension of the channels (not shown). It is to beunderstood that a liquid holding formation may constitute an entireabsorbent core, but as illustrated, the liquid holding formation 89 issurrounded by a thinner outer region 93 also forming part of theabsorbent core 87. The channels 91 facilitate distribution of fluid inthe liquid holding formation 89. Notably, the channels 91 terminateprior to reaching a peripheral edge 93 of the liquid holding formation89 which surrounds the channels. This construction helps prevent thefluids from running in the channels 91 completely off of the liquidholding formation 89 before they are absorbed. The channels 91 areformed by ridges on the bottom surface of the forming surface which areclosely similar to the ridges 83 shown in FIGS. 4 and 5 which formed thechannels 40 of the liquid holding formation 38A. However, the ridgesstop short of a transition surface (similar to transition surface 81) inthe pocket, thereby spacing the ends of the channels 91 from the edge ofthe liquid holding formation 89.

It will be appreciated that details of the foregoing embodiments, givenfor purposes of illustration, are not to be construed as limiting thescope of this invention. Although only a few exemplary embodiments ofthis invention have been described in detail above, those skilled in theart will readily appreciate that many modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of this invention. For example, featuresdescribed in relation to one embodiment may be incorporated into anyother embodiment of the invention. Accordingly, all such modificationsare intended to be included within the scope of this invention, which isdefined in the following claims and all equivalents thereto. Further, itis recognized that many embodiments may be conceived that do not achieveall of the advantages of some embodiments, particularly of the preferredembodiments, yet the absence of a particular advantage shall not beconstrued to necessarily mean that such an embodiment is outside thescope of the present invention.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. An absorbent core comprising an elongate liquid holding formationwith a peripheral edge, the liquid holding formation comprising afibrous material composed at least in part of cellulosic fibers andhaving a surface formed with at least one longitudianlly extendingchannel in the fibrous material for distributing liquid lengthwise alongthe core, the channel having longitudinally opposite ends spacedlongitudinally inward from the peripheral edge of the liquid holdingformation to inhibit the flow of liquid in the channels past theperipheral edge of the liquid holding formation, said cellulosic fibersbeing distributed throughout the thickness of the liquid holdingformation.
 2. An absorbent core as set forth in claim 1 furthercomprising an outer region of fibrous material located outward of theperipheral edge of the liquid holding formation, the outer region beingthinner than the liquid holding formation.
 3. An absorbent core as setforth in claim 1 wherein the absorbent core includes an upper surfaceand a lower surface opposed to the upper surface, the upper surfacehaving the channels formed therein, the lower surface beingsubstantially flat.
 4. An absorbent core as set forth in claim 1 furthercomprising an outer region of fibrous material located outward of theperipheral edge of the liquid holding formation.
 5. An absorbent core asset forth in claim 4 wherein the absorbent core has a width and a lengthgreater than said width, the outer region of the absorbent core having,in cross-section taken across the width of the absorbent core, a firstthickness, the liquid holding formation having a second thicknessgreater than the first thickness.
 6. An absorbent core as set forth inclaim 5 wherein the absorbent core further comprises a transitionportion connecting the outer region and the liquid holding formation. 7.An absorbent core as set forth in claim 1 wherein the liquid holdingformation has a surface area that is at least about 10% greater than aprojected surface area of the liquid holding formation.
 8. An absorbentcore as set forth in claim 1 wherein the core comprises an air formedfibrous material.
 9. An absorbent article comprising an absorbent coreas set forth in claim
 1. 10. An absorbent article as set forth in claim9 wherein the absorbent article is selected from a group consisting of adisposable diaper, a training pant, a feminine care article, and anincontinence article.